Corrosion behavior in aluminum/galvanized steel resistance spot welds and self-piercing riveting joints in salt spray environment

Abstract

This paper underlined the corrosion behavior of aluminum alloy/galvanized steel joints fabricated by resistance spot welding (RSW) and self-piercing riveting (SPR) exposed to different salt-spray cycles. It was found that the crevice generated by different joining methods has an important impact on corrosion behavior. Compared with the RSW joint, less corrosion happened on the coupled regions in SPR joints because of the higher local pH value resulted from the smaller crevice. The crevice, however, has less impact on the types of corrosion products. Galvanic corrosion happened in the coupled region for both RSW and SPR joints. The Pourbaix diagram explained the stable corrosion products of Al and ZnFe alloy, which are Al2O3, ZnO, and Fe3O4. Additional corrosion products observed from the experiment included α-Al(OH)3, Ca4Al2(CO3)(OH)12(H2O)5, Zn5(OH)8Cl2(H2O), Zn5(CO3)2(OH)6, and Fe2(OH)2(CO3), which can be understood by considering the metastable corrosion products, Pourbaix diagram, and possible chemical reactions.